Proteins which are secreted are highly interesting for use in industrial applications. A positive selection screening system which selects only host cells secreting proteins is thus very desirable.
Signal trapping is a method to identify genes containing a signal peptide using a translational fusion to an extracellular reporter gene lacking its own signal. This has been reported in the literature for the purpose of identifying new signal sequences (Smith, H. et al., 1987, Construction and use of signal sequence selection vectors in Escherichia coli and Bacillus subtilis. J. Bact. 169:3321-3328), also the use of such for defining clearly the specific elements within signal peptides which are required for optimal function (Smith, H. et al, 1988. Characterisation of signal-sequence-coding regions selected from the Bacillus subtilis chromosome. Gene. 70:351-361).
A further development, signal sequence trapping, has been described in WO 01/77315 (Novozymes A/S).
HtrA-type serine proteases participate in folding and degradation of aberrant proteins and in processing and maturation of native proteins (Pallen M J; Wren B W (1997): The HtrA family of serine proteases. Molecular microbiology 26: 209-221). It has been shown that the Bacillus subtilis YkdA and YvtA, members of this family are induced by secretion stress; when cells are expressing and secreting heterologous amylases (Noone D, Howell A, Collery R, and Kevin M. Devine (2001): YkdA and YvtA, HtrA-Like Serine Proteases in Bacillus subtilis, Engage in Negative Autoregulation and Reciprocal Cross-Regulation of ykdA and yvtA Gene Expression. Journal of Bacteriology 183: 654-663). This secretion stress induction happens at the transcriptional level.